Colour temperature is a characteristic of visible light and usually determined by comparing its chromaticity with an ideal black-body radiator. The measurement for colour temperature is Kelvin (K). Examples of warm colours (with lower Kelvin value) are yellow and red while examples of cool colours (with higher Kelvin value) are blue and green. Warmer colour temperatures are suitable for living spaces while cooler colour temperatures are suitable for visual tasks. Recommended colour temperatures for general indoor and task lighting are in the 2580K-3710K range.
CCT is the colour temperature of the black body radiator which has the closest matches to the light from the lamp to the human colour perception. This is because the lighting sources emit light primarily by mean of processes rather than increasing the temperature of the body.
Visible white light consists of electromagnetic radiation of various wavelengths. The colours are conventionally divided into red, orange, yellow, green, blue, indigo, and violet. Red, green and blue light are additive primary colours, which in combination will produce almost all colours, including white.
An impression of white light can be created by mixing appropriate intensities of primary colours of light (red, green and blue), a process called additive mixing as seen in many display technologies. Computer displays often have a colour temperature control, allowing user to select the colour temperature (usually from a small set of fixed values) of the light emitted when the computer produces the electrical signal corresponding to “white”.
Solid state lighting that utilizes light emitting diodes as sources is replacing electrical filaments or gas because it creates visible light with reduced heat generation or parasitic energy dissipation and more resistance to shock and wear, therefore increasing the lifespan.
Light emitting diode (LED) lamp is a type of solid state lighting that comprises light emitting diodes as source of lighting instead of electrical filaments or gas. LED lamps usually contain clusters of LEDs in an appropriate housing. The housing used for the LED lamp usually has an opening to direct the light from the LEDs to the intended direction. The said housing opening is usually made of transparent material in order to transfer a large percentage of light beams from the LED lamp to the intended space.
U.S. Pat. No. 6,741,35, discloses a white light emitting luminaire with light sensor configurations for optical feedback. The luminaire includes a condenser lens to direct the combined light output from the array of LEDs to a target light guide, which has a partial reflecting element to reflect certain portion of the light output from the condenser lens back towards the LED array. The specification of U.S. Pat. No. 6,741,351 is hereby incorporated by reference into this specification.
The arrangement in U.S. Pat. No. 6,741,351, needed an extra condenser lens and partial reflecting element in order to reflect back a small percentage of light back to towards the LED array. There is a need for a more efficient and cost effective method to reflect the light back the LED array by having less components.
Furthermore, the angle of lighting from the each LED is usually in the range of 90°-120°, which is relatively wide. Although this wide angle light can be used to light up a larger area, high energy consumption is needed in order to light the area because a wide angle of lighting will lead to divergence of light and causes low brightness.
Due to the fact that LED can only produce one single colour, there are a few methods to convert it into white light. The first method is wavelength conversion, wherein LED colours are accompanied with phosphors of different colour. For example, blue LED with yellow phosphor, blue LED with several colours of phosphors, ultraviolet LED with red, green and blue phosphors, or blue LED with quantum dots.
The second method is colour mixing, wherein the usage of a plurality of LEDs with different colours, combined together in the correct proportion in order to produce white light. Several combinations can be done, such as two LEDs of blue and yellow colour; three LEDs of red, blue and green; or four LEDs of red, blue, green and yellow. Since no phosphors are used for this method, there will be no energy loss in conversion process, resulting in higher efficiency. Although a colour mixing concept of single colour LEDs such as red, green, blue and yellow can be used to create white light, the brightness of each LED is limited compared to white LED. Therefore, using colour mixing of single colour LEDs will need extra energy or higher quantity in order to create the same luminous flux as white LEDs with different CCT ranges.
White LED is created by having a blue LED and a phosphor coating to mix yellow light with blue in order to produce light that appears to be white. Nevertheless, if white LED is used alone in the LED lamp, the colour temperature of the said LED lamp cannot be controlled because LED can degrade in time. Degradation happens especially to phosphor based LEDs due to the heat loss from the Stokes shift. Furthermore, the different phosphors used in white LEDs, which will degrade with heat and age, but at different rates will cause changes to the produced CCT of the light output.
If a certain confined room contains several white LED lamps, which will degrade at different rates due to heat and age, there will be inconformity between the lamps, which may create undesirable CCT to the room given time. The usual solution to this problem would be to either change the white LED lamps or change the LED components in the lamp, which incurs extra cost and manpower.
Another condition whereby a certain confined room may have white LED lamps of inconsistent CCT is when the room comprises of new and old LED lamps, LED lamps from different manufacturing bins or batches or comprises of different models of LED lamps. Conventionally, one way to solve the problem of CCT inconsistency among several LED lamps in the same room due to the different degrading speed of each LED lamps is to order LED lamps from a narrower manufacturing bin, wherein manufacturers will choose the LEDs from a narrower bin to ensure LED lamps do not degrade too extensively among each other.
Different CCT of white lighting is suitable for different usage in the space of lighting. For example, warmer colour temperature is suitable for living spaces while cooler colour temperature is suitable for visual tasks. Different user of lighting space will have different preference on the CCT of the white lighting. If the same space of lighting is used for different purposes and different users, there is a need to have an easy way to change the CCT of the white lighting source. Nevertheless, if a white LED lamp contains only white LEDs, the user will not be able to control the CCT of the lamp because white LEDs have fixed CCT, unless the user changes the hardware (ie white LEDs) in the lamp to produce different CCT.
Due to the different degradation rate of LED lamps in a single room, possibility of having old and new LED lamps in the same room, possibility of having LED lamps of different manufacturing bins or batches, and possibilities of having different models of LED lamps, which leads of inconsistency in the CCT in the room, there is a need to maintain the desired CCT of light beam that is being emitted from the LED lamps, without the need for any hardware replacement.
The present invention overcomes, or at least partly alleviates the above shortcomings by providing a methodology of maintaining CCT of light beam from lighting means such as LED lamp, wherein steps comprising: transmitting light from lighting means through confined space, having a percentage of said light transmitted back towards sensory means by reflecting means having sensory means located behind the lighting means to capture reflected light beam, having sensory means to read CCT of reflected light beam, having sensory means to convert CCT reading into binary data, having at least one any acceptable processing means to compare binary data obtained from sensory means against intended CCT binary data, having said processing means to instruct said lighting means to transmit lower CCT of lighting beam if obtained CCT binary is higher than the intended CCT binary data for a certain acceptable threshold to maintain intended CCT to be transmitted from the light means; or vice versa; and repeating the steps mentioned continuously throughout operation duration.
The present invention also overcomes, or at least partly alleviates the above shortcomings by providing a methodology of creating lighting of white colour with intended CCT, whereby the usage of any combination of cool white, white, warm white and amber LEDs with CCT ranges of 5000K and 7000K, 3700K and 5000K, 2500K and 3700K, and DWL ranges of 585 nm and 595 nm are used in the LED lamp; furtherance comprising a processing means in order to control the CCT of the lighting source depending on the preference and usage of the user.
The present invention also overcomes, or at least partly alleviates the above shortcomings by providing a methodology of light feedback system for lighting means, whereby the light that is transmitted from the lighting means such as LED array is being reflected back to the sensory system located at the back of the LED array by a reflecting means, which is part of the housing; said sensory system comprises a light guide with a large viewing angle and a colour sensor; and said light from the lighting means can be transmitted through an optional focus lens to provide a narrower lighting angle (e.g. 10° (spot model) or 30° (flood model) viewing angle).